In the following the invention will be explained in relation to a Solid Oxide Fuel Cell. The interconnect according to the invention can, however, also be used for other types of fuel cells such as Polymer Electrolyte Fuel cells (PEM) or a Direct Methanol Fuel Cell (DMFC).
A Solid Oxide Fuel Cell (SOFC) comprises a solid electrolyte that enables the conduction of oxygen ions, a cathode where oxygen is reduced to oxygen ions and an anode where hydrogen is oxidised. The overall reaction in a SOFC is that hydrogen and oxygen electrochemically react to produce electricity, heat and water. In order to produce the required hydrogen, the anode normally possesses catalytic activity for the steam reforming of hydrocarbons, particularly natural gas, whereby hydrogen, carbon dioxide and carbon monoxide are generated. Steam reforming of methane, the main component of natural gas, can be described by the following equations:CH4+H20CO+3H2 CH4+CO22CO+2H2 CO+H20CO2+H2 
During operation an oxidant such as air is supplied to the solid oxide fuel cell in the cathode region. Fuel such as hydrogen is supplied in the anode region of the fuel cell. Alternatively, a hydrocarbon fuel such as methane is supplied in the anode region, where it is converted to hydrogen and carbon oxides by the above reactions. Hydrogen passes through the porous anode and reacts at the anode/-electrolyte interface with oxygen ions generated on the cathode side that have diffused through the electrolyte. Oxygen ions are created in the cathode side with an input of electrons from the external electrical circuit of the cell.
To increase voltage, several cell units are assembled to form a stack and are linked together by interconnects. Interconnects serve as a gas barrier to separate the anode (fuel) and cathode (air/oxygen) sides of adjacent cell units, and at the same time they enable current conduction between the adjacent cells, i.e. between an anode of one cell with a surplus of electrons and a cathode of a neighbouring cell needing electrons for the reduction process. Further, interconnects are normally provided with a plurality of flow paths for the passage of reactant gasses: fuel gas on one side of the interconnect and oxidant gas on the opposite side.
US 20040219423 describes an internal manifolding interconnect made from for instance a stainless steel metal sheet with a thickness of 0.1-2 mm. The sheet can be stamped to provide raised ridges and/or dimples defining the flow paths on both sides of the interconnect.
EP 1300901 describes interconnects where plastic deformation is used to obtain good electrical contact.
EP 1444749 describes how it is preferred to have current collectors/distributors reaching a plastic-type deformation comprised between 30% and 40% of their initial thickness once the assembling is completed. In this way, a uniform contact pressure close to the optimum operation condition is safely established.
U.S. Pat. No. 6,605,381 describes how another layer can be added between the outside layer and the projecting ribs of the current collector plate. The purpose for such a layer consists of keeping the electric contact resistance to the channel structure as low as possible. For this, the layer could be deformable by plasticity or elasticity thereby allowing that the dimensional tolerances of the current collector plates or, in the case of an arrangement in a fuel cell stack, of the bipolar plates are compensated for and the current collection from the gas diffusion structure can occur evenly.